This is the National phase Application of PCT/J199/03653, filed Jul. 6, 1999.
The present invention relates to an alkaline earth metal salt of a xcex2-diketo compound which is used as an auxiliary for resin molding, and to a method for producing the same.
Alkaline earth metal salts of xcex2-diketo compounds (hereinafter, referred to as xcex2-diketo compound salts or salts of xcex2-diketo compounds) are utilized as auxiliaries for resin molding, particularly, as nonpoisonous or nontoxic stabilizers for vinyl chloride resin molding.
Various methods for producing the xcex2-diketo compound salt are known. For example, Zh. Neorg. Khim. (1990), 35(11), 2776-80 discloses a method for producing a xcex2-diketo compound salt by a reaction between acetylacetone and calcium chloride or calcium nitrate. However, the method is disadvantageous in terms of quality, because it is necessary to remove impurities such as a chloride and a nitrate (or anitric acid salt) contaminating the resulting xcex2-diketo compound salt (acetylacetonato).
Japanese Patent Publication No. 24777/1985 (JP-B-60-24777) describes a method for producing a xcex2-diketo compound salt by adding an alkaline earth metal hydroxide to a xcex2-diketo compound (e.g., acetylacetone) in a ratio of 1 mol of the former to the equivalent (2 mol) of the latter. However, according to this method, the viscosity rises in the latter half of the reaction, increasing the load on the power that the mixer requires. For such reasons, the method involves an expensive reactor, and thus is industrially disadvantageous. Further, the xcex2-diketo compound salt thus obtained is not suitable for use as a stabilizer, because the salt contains about 6 to 7% by weight of moisture (corresponding to one molecule of water of crystallization). For example, when a stabilizer containing water of crystallization is used in molding a vinyl chloride resin, bubbling due to water vapor remarkably deteriorates the strength and clarity (transparency) of the vinyl chloride resin. Furthermore, since the stability of the xcex2-diketo compound salt produced in accordance with the process of the literature is low, the salt cannot be preserved for long periods of time. For example, when a calcium salt of acetylacetone produced according to the method is dried to a water (moisture) content of 1% by weight or less, the purity of the salt is remarkably lowered from 97% by weight to 86% by weight in a month.
Furthermore, German Patent DE96-19610320 describes a method for producing a xcex2-diketo compound salt by adding a xcex2-diketo compound (e.g., acetylacetone) to an alkaline earth methyl hydroxide in the absence of a solvent using 1 mol of the latter and the equivalent (2 mols) of the former. In the method described in this literature, the xcex2-diketo compound is added to the alkaline earth metal hydroxide and reacted at 40xc2x0 C. or lower, thus preventing the viscosity of the reaction mixture from becoming too high and making it possible to react the reaction mixture in the form of particles or powder. However, according to the method of the literature, the xcex2-diketo compound needs to be added slowly in order to prevent the viscosity from becoming too high. Therefore, it takes time to complete the reaction, the conversion is low (for example, about 94% when hydrated lime is used), and the resulting xcex2-diketo compound salt is of lower purity.
Accordingly, it is an object of the present invention to provide highly stable xcex2-diketo compound salts of higher quality and a method for producing the same.
It is another object of the present invention to provide, regardless of a reactant being reacted in powdery form (or in the form of particles), a method whereby xcex2-diketo compound salts of high purity can industrially advantageously be produced at high conversions without an increase in viscosity.
It is still another object of the present invention to provide a method for effectively producing xcex2-diketo compound salts within a short period of time without lowering the conversion and purity.
The inventors of the present invention have found that, when an alkaline earth metal hydroxide such as calcium hydroxide remains unreacted, the purity of a xcex2-diketo compound salt is remarkably decreased during its preservation probably because of the condensation of an acetylacetone unit of the xcex2-diketo compound salt. Based on such knowledge, the inventors did intensive research to achieve the above objects, and finally found that, when an aliphatic xcex2-diketo compound is used in an excess amount relative to the amount of an alkaline earth metal compound, the resulting xcex2-diketo compound salt is of high purity and highly stable. The present invention was accomplished based on the above findings.
In summary, the present invention is a method for producing an alkaline earth metal salt of a xcex2-diketo compound from a powdery alkaline earth metal compound and an aliphatic xcex2-diketo compound, wherein 2.04 mol or more of the aliphatic xcex2-diketo compound is used relative to 1 mol of the alkaline earth metal compound. The reaction may be carried out while supplying the alkaline earth metal compound and the aliphatic xcex2-diketo compound continuously or intermittently, or by adding one component to the other continuously or intermittently. The total amount of each component used need only be within the above range, and the amount of each component in a reaction stage or a supply stage need not be within the above range. Furthermore, the highest temperature throughout the reaction may be 50xc2x0 C. or higher, and a drying operation may be conducted at 100 to 180xc2x0 C. in an atmosphere of an inert gas. The alkaline earth metal compound may be calcium hydroxide, magnesium hydroxide, or barium hydroxide. Moreover, the aliphatic xcex2-diketo compound may be represented by the following formula (1): 
wherein R1 and R2 are same or different, each representing hydrogen atom, a C1-6 alkyl group, or a C1-10 alkoxy group,
or may be an acetoacetic acid C1-4 alkyl ester or acetylacetone.
Furthermore, the alkaline earth metal salt of the xcex2-diketo compound of the present invention is produced according to the method as described above. The alkaline earth metal salt of a xcex2-diketo compound contains 1% by weight or less of water (moisture) and has a purity of not less than 98% by weight.
[Alkaline earth metal compound]
As the alkaline earth metal compound, there may be exemplified hydroxides of alkaline earth metals (for example, magnesium hydroxide, calcium hydroxide, and barium hydroxide). These alkaline earth metal compounds may be used singly or as a combination of two or more species.
The alkaline earth metal compound may be used in the form of particles or in powdery form. Those commercially available for industrial use may be used as they are. The mean particle size of the alkaline earth metal compound is about 0.1 to 300 xcexcm, preferably about 0.1 to 150 xcexcm.
Further, it is preferred that the alkaline earth metal compound contains little or no impurities (e.g., silica, alumina, alkaline earth metal carbonates). The amount of impurities is, for example, 2% by weight or less, preferably 1% by weight or less, more preferably 0.5% by weight or less.
[Aliphatic xcex2-diketo compound]
As the aliphatic xcex2-diketo compound, compounds of the formula (1) may be used. In the formula (1), R1 and R2 may be same or different, each representing a hydrogen atom, a C1-6 alkyl group (for example, C1-4 alkyl groups such as methyl and ethyl groups), or a C1-10 alkoxy group (for example, C1-6 alkoxy groups such as methoxy, ethoxy, propoxy and butoxy groups). For example, there are exemplified compounds having a 2,4-alkanedione or acetoacetic acid ester structure.
Preferred aliphatic xcex2-diketo compounds are compounds represented by the formula (1) wherein R1 is a C1-4 alkyl group (e.g., methyl group, ethyl group) and R2 is a C1-4 alkyl group (e.g., methyl group, ethyl group) or C1-6 alkoxy group (e.g., methoxy, ethoxy, propoxy and butoxy groups). Even when both R1 and R2 are C1-4 alkyl groups, they may be the same or different C1-4 alkyl groups. Included among the particularly preferred aliphatic xcex2-diketo compounds are acetylacetone and acetoacetic acid C1-4 alkyl esters (e.g., methyl acetoacetate, ethyl acetoacetate).
Commercially available aliphatic xcex2-diketo compounds for industrial use may be employed as they are.
According to the present invention, since an excess of an aliphatic xcex2-diketo compound is used relative to the amount of an alkaline earth metal compound, there is produced a highly stable xcex2-diketo compound salt of high purity regardless of reaction method. In other words, according to the present invention, the aliphatic xcex2-diketo compound is used in an amount of not less than 2.04 mol, for example, about 2.04 to 5 mol (for example, about 2.05 to 4.5 mol), preferably about 2.1 to 4 mol (for example, about 2.1 to 3 mol), more preferably about 2.2 to 2.8 mol (for example, about 2.2 to 2.6 mol), relative to 1 mol of the alkaline earth metal compound. The amount of the remaining alkaline earth metal compound is reduced by merely using the aliphatic xcex2-diketo compound in an amount slightly exceeding 2 mol. However, when the aliphatic xcex2-diketo compound is used too much, the viscosity of the reaction mixture becomes high (i.e., like a viscous paste) at near the end of the reaction, and therefore it is difficult to stir the mixture.
[Reaction]
According to the present invention, salts of xcex2-diketo compounds can be produced by reacting the xcex2-diketo compound with the alkaline earth metal compound while maintaining the flowability of the powder (or particles).
The reaction between the alkaline earth metal compound and the xcex2-diketo compound can be carried out by supplying the alkaline earth metal compound and the xcex2-diketo compound to a reactor continuously or intermittently. For example, the reaction between the alkaline earth metal compound and the xcex2-diketo compound can be performed by supplying these compounds to a reactor capable of mixing (apparatuses for kneading or blending powders, such as kneaders, channel-type dryers, ribbon blenders) via a feeder or supplying machine (e.g., metering supply machine).
When continuously or intermittently supplying the alkaline earth metal compound and the aliphatic xcex2-diketo compound to the reactor, each component may be supplied to the reactor in the aforementioned proportion, or each component may be supplied such that the proportion of the component at the end of the supply (the total of each component used) is within the range mentioned above.
Alternatively, the reaction may be effected by adding, between the alkaline earth metal compound and the aliphatic xcex2-diketo compound, one component to the other. Though possible to provide highly stable xcex2-diketo compound salts of high purity by adding the xcex2-diketo compound to the alkaline earth metal compound continuously or intermittently, the reaction mixture may sometimes grow viscous in the latter half of the reaction. Accordingly, it is advantageous to carry out the reaction by adding the aliphatic xcex2-diketo compound to the alkaline earth metal compound continuously or intermittently. In the case of adding the aliphatic xcex2-diketo compound, the method has the advantage of maintaining the mixture in a powdery state throughout the whole procedure, i.e., from the reaction step to the drying step.
As the manner in which the xcex2-diketo compound is added, there may be mentioned a method which comprises steps of charging a reactor capable of mixing (e.g., apparatuses for kneading or blending powders, such as kneaders, channel-type dryers, ribbon blenders) with the particles or powder of alkaline earth metal hydroxide, and then adding the xcex2-diketo compound continuously or intermittently while stirring the particles or powder.
When adding one component (for example, the alkaline earth metal compound) to the other (for example, the aliphatic xcex2-diketo compound) continuously or intermittently, the proportion of each component at the end of the reaction (the total amount of each component used) need only be within the range set forth.
Since the reaction between the alkaline earth metal compound and the aliphatic xcex2-diketo compound is an exothermic reaction, the reaction is usually performed while controlling the reaction temperature by removing the reaction heat by means of cooling (e.g., jacket cooling). The reaction temperature is, for example, about 0 to 100xc2x0 C., preferably about 30 to 100xc2x0 C., more preferably about 60 to 80xc2x0 C. A reaction temperature exceeding 100xc2x0 C. causes the loss of the aliphatic xcex2-diketo compound, leading to a consequent reduction in the conversion of the alkaline earth metal compound. As a result, the quality of the resulting xcex2-diketo compound salt (color, purity, stability, etc.) is deteriorated.
In the reaction step, it is preferred that the highest temperature during the reaction is kept at 50xc2x0 C. or higher (for example, about 50 to 100xc2x0 C.), 55xc2x0 C. or higher (for example, about 55 to 95xc2x0 C., particularly about 55 to 80xc2x0 C.). When the highest temperature in the reaction is 50xc2x0 C. or higher, since the conversion rate of the alkaline earth metal compound is raised, the resulting salt of the xcex2-diketo compound is improved in terms of purity and stability.
The reaction may be is carried out in a batch system, a semibatch system or a continuous system.
[Aging]
The reaction mixture obtained batchwise or semi-batchwise may be subjected to an aging if necessary. Aging of the reaction mixture further increases the conversion rate of the alkaline earth metal compound. The temperature for aging is, about 40 to 100xc2x0 C., preferably about 50 to 90xc2x0 C., more preferably 60 to 80xc2x0 C. When the temperature for aging exceeds 100xc2x0 C., the quality of the resulting xcex2-diketo compound salt (e.g., color, purity, stability) is deteriorated due to the loss of the aliphatic xcex2-diketo compound.
The aging time may suitably be selected. The aging time is usually 1 hour or longer, preferably about 1 to 24 hours (for example, 1 to 16 hours), more preferably about 4 to 12 hours. Alternatively, the time may be about 2 to 8 hours.
[Drying]
The reaction mixture usually contains water of crystallization and water generated during the reaction [for example, 2 mol of by-product water is generated when 1 mol of hydrated lime is used]. Accordingly, the salt of the xcex2-diketo compound is obtained by drying the reaction mixture, directly after the reaction or after completion of the aging, for removing the by-produced water or the water of crystallization.
The drying may be carried out in an atmosphere of an inert gas (for example, nitrogen, helium, carbon dioxide), preferably under a flow (or a stream) of an inert gas (for example, while blowing an inert gas to a reactor). When dried in the air, the product is colored due to the oxidation or condensation of the xcex2-diketo compound. If necessary, the drying operation is performed under reduced pressure.
The drying temperature (when drying while elevating the temperature, this term refers to the finally reached temperature) is usually about 100 to 180xc2x0 C., preferably about 100 to 150xc2x0 C. (for example, about 120 to 150xc2x0 C.). When the drying temperature is lower than 100xc2x0 C., it is difficult to remove the water of crystallization. Furthermore, insofar as the xcex2-diketo compound salt is not decomposed, the drying temperature can be selected according to the species of the xcex2-diketo compound salt. As to the representative xcex2-diketo compound salts, their preferable drying temperatures are shown in Table 1.
An excess of the xcex2-diketo compound can be removed by drying. The removed xcex2-diketo compound can be condensed and trapped (or collected) together with the by-produced water using a condenser or the like, and the trapped xcex2-diketo compound is reusable for reactions using other portions of alkaline earth metal compound.
The drying may be performed either in the reactor mentioned above, or in a batch system, a semibatch system or a continuous system.
In the present invention, it is preferred that the powdery alkaline earth metal compound and the xcex2-diketo compound are continuously supplied and dried. The use of an excessive amount of the xcex2-diketo compound relative to the amount of the alkaline earth metal compound and continuous supply of the components make it possible, with industrial advantages, to produce xcex2-diketo compound salts within a short period of time without lowering the quality, and therefore the method of the present invention is economically advantageous. If necessary, the aging operation may be performed.
When the aliphatic xcex2-diketo compound is continuously or intermittently added to the powdery alkaline earth metal compound, for providing a xcex2-diketo compound salt of high quality, it is preferred that 2.1 to 3 mol of the xcex2-diketo compound relative to 1 mol of the alkaline earth metal compound is used; the aging is performed if necessary; and that the resulting salt is dried at 100 to 150xc2x0 C. in an atmosphere of an inert gas.
The salt of xcex2-diketo compound thus obtained is of high purity, and the purity of which is usually 98.0% by weight or more. Further, the water (moisture) content of the salt is 1% by weight or less, preferably 0.8% by weight or less, more preferably 0.5% by weight or less, and usually about 0.1 to 0.8% by weight (particularly, about 0.1 to 0.5% by weight). Furthermore, the amount of impurities is 2% by weight or less, preferably 1.8% by weight or less, more preferably 1.5% by weight or less, and usually about 0.1 to 1.8% by weight (particularly, about 0.1 to 1.5% by weight). Since the content of impurities is low, the xcex2-diketo compound salt of the present invention is highly stable.
According to the present invention, since the alkaline earth metal content of the xcex2-diketo compound salt is reduced, highly stable xcex2-diketo compound salts of high quality are consequently provided. Further, xcex2-diketo compound salts of high purity can industrially advantageously be produced at high conversions. Furthermore, xcex2-diketo compound salts of high quality can be produced within a short period of time by reacting an alkaline earth metal compound with a xcex2-diketo compound while supplying them continuously, and therefore the method of the present invention is economically advantageous. Thus, the xcex2-diketo compound salt of the present invention can be utilized as a stabilizer for vinyl chloride resins. Particularly, since its moisture content is low, the salt is available for use as a low-effervescent stabilizer. Moreover, the xcex2-diketo compound salt can stably be used over long periods of time due to its high stability.